1. Field of the Invention
The present invention relates to a thermally-assisted magnetic recording head for use in thermally-assisted magnetic recording to write data on a recording medium with the coercivity thereof lowered by irradiating the recording medium with near-field light.
2. Description of the Related Art
Recently, magnetic recording devices such as magnetic disk drives have been improved in recording density, and thin-film magnetic heads and recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a read head unit including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider configured to slightly fly above the surface of a recording medium. The slider has a medium facing surface configured to face the recording medium. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end).
Here, the side of the positions closer to the leading end relative to a reference position will be referred to as the leading side, and the side of the positions closer to the trailing end relative to the reference position will be referred to as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the recording medium smaller. Making the magnetic fine particles smaller, however, causes the problem that the magnetic fine particles drop in the thermal stability of magnetization. To eliminate this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the recording medium, and this makes it difficult to perform data writing with existing magnetic heads.
To resolve the foregoing problems, there has been proposed a technology called thermally-assisted magnetic recording. The technology uses a recording medium having high coercivity. When writing data, a write magnetic field and heat are simultaneously applied to the area of the recording medium where to write data, so that the area rises in temperature and drops in coercivity for data writing. The area where data is written subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization. Hereinafter, a magnetic head for use in thermally-assisted magnetic recording will be referred to as a thermally-assisted magnetic recording head.
In thermally-assisted magnetic recording, near-field light is typically used as a means for applying heat to the recording medium. A known method for generating near-field light is to use a plasmon generator, which is a piece of metal that generates near-field light from plasmons excited by irradiation with laser light. The laser light to be used for generating near-field light is typically guided through a waveguide, which is provided in the slider, to the plasmon generator disposed near the medium facing surface of the slider.
U.S. Patent Application Publication No. 2011/0170381 A1 discloses a thermally-assisted magnetic recording head including a main pole, a waveguide and a plasmon generator. The main pole has an end face located in the medium facing surface, and produces a write magnetic field from the end face. The plasmon generator has a near-field light generating surface located in the medium facing surface. The waveguide includes a core and a cladding. In this head, the surface of the core and the surface of the plasmon generator face each other with a gap interposed therebetween. This head is configured to excite surface plasmons on the plasmon generator by using evanescent light that occurs on the surface of the core based on the light propagating through the core, and to cause near-field light to be generated from the near-field light generating surface based on the excited surface plasmons.
A thermally-assisted magnetic recording head suffers from the problem that heat generated by the plasmon generator causes the plasmon generator to shrink and become distant from the medium facing surface, and also causes the main pole to be corroded, which result in a shorter life of the thermally-assisted magnetic recording head.
In order to achieve higher recording density, it is essential to make the track width smaller. Making the track width smaller increases the track density. A thermally-assisted magnetic recording head including a plasmon generator allows the plasmon generator to form a spot of near-field light on a recording medium. The size of the spot of near-field light will hereinafter be referred to as light spot size. It has conventionally been considered that a smaller light spot size is effective for achieving higher recording density. In order to make the light spot size smaller, it is effective to reduce the width of the near-field light generating surface of the plasmon generator.
U.S. Patent Application Publication No. 2011/0170381 A1 discloses a plasmon generator including a narrow portion and a wide portion. The narrow portion includes the near-field light generating surface located in the medium facing surface. The wide portion is located farther from the medium facing surface than is the narrow portion. Here, we define a neck height as the length of the narrow portion in a direction perpendicular to the medium facing surface. In the plasmon generator disclosed in U.S. Patent Application Publication No. 2011/0170381 A1, heat generated at the narrow portion, particularly at the near-field light generating surface, may cause the narrow portion to shrink and become distant from the medium facing surface, and consequently cause the plasmon generator to become unable to form a sport of near-field light on a recording medium. A conceivable countermeasure to prevent this is to reduce the neck height. Reducing the neck height can enhance the heat sink effect of the wide portion to dissipate the heat generated at the narrow portion. Reducing the neck height can also increase the efficiency of generation of near-field light.
Conventionally, however, any attempts to reduce the neck height have resulted in difficulty in accurately controlling the width of the near-field light generating surface.